Helix angle sensor and roll control means



Nov. 10, 1964 R. P. WHITE HELIX ANGLE SENSOR AND ROLL CONTROL MEANSFiled June 20. 1960 SERVO PROGRAM ACTUATOR TRANSDUCER COMPARATOR l4 Flg.2

V 32 TRANSDUCER TRANSDUCER PROGRAM COMPUTER COMPARATOR 22 6a 28 36 30ERROR v 34 T o AMPLIFIER CALIBRATOR SERVO 4 ACTUATOR Flg. 3 INVENTOR. 8RICHARD P. WHITE i T BY Mam United States Patent 3,156,436 HELEX ANGLESENSOR AND ROLL CGNTRGL MEANS Richard P. White, San Diego, Calif,assignor to Ryan Aeronautical (10., San Diego, Calif. Filed June 29,1am, Ser. No. 37,339 3 Claims. (ill. 244-44) The present inventionrelates generally to aerodynamic controls and more particularly to ahelix angle sensor and roll control means.

The primary object of this invention is to provide a free floating,weathercocking vane for attachment to an aerodynamic vehicle, inparticular a ballistic missile, to sense the helix angle or roll rate inrelation to speed of the missile and, through a simple control system,to apply a correcting action by means of aerodynamic roll controlsurfaces to aid in maintaining the missile on course.

An ancillary object of this invention is to provide a helix angle sensorwhich is used in conjunction with velocity indicating means, in order tocontrol the roll rate in proportion to the missile velocity for properstabilization of the ballistic trajectory.

A further object of this invention is to provide a sensor for supplyinga signal proportional to the rate of roll, the signal being compared toa program signal corresponding to the required roll rate and theresultant difference or error signal being utilized to operate the rollcontrol surfaces'and correct any difference.

Finally, it is an object to provide a helix angle sensor and rollcontrol means of the aforementioned character which is simple andconvenient to assemble and install and which will give generallyeflicient and accurate results over a wide range of operatingconditions.

With these and other objects definitely in view, this invention consistsin the novel construction, combination and arrangement of elements andportions, as will be hereinafter fully described in the specification,particularly pointed out in the claims, and illustrated in the drawingwhich forms a material part of this disclosure, and in which:

FIGURE 1 is a perspective view of a typical ballistic missileincorporating the helix angle sensor;

FIGURE 2 is a block diagram of the simplified control system; and

FIGURE 3 is a block diagram of a complete control system with a velocitysensing means.

Similar characters of reference indicate similar or identical elementsand portions throughout the specification and throughout the views ofthe drawing.

The helix angle sensor includes a free floating, weathercocking vane 10,pivotally mounted on the body of a missile 12, so as to be fully exposedto the airstream flowing around the missile in flight. Any angulardisparity between the longitudinal axis of the missile along its flightpath and the direction of airflow causes deflection of the vane from itsstable or neutral position in which the vane chordal axis is parallel tothe missile longitudinal axis. Since in stable ballistic flightthemissile is effectively at zero angle of attack, any deviation of thevane 10 must be caused by rolling or rotation of the missile about itslongitudinal axis, the vane thus sensing the helical airflow due to thecombination of roll and forward motion. Weathercocking vanes haveheretofore been used to detect drift, yaw, or similar deviations ofaircraft, but these are static conditions. In the present apparatus, thevane 10 senses a dynamic condition, the rate of roll.

In actuality, the vane 10 senses the helix angle, which is thehypothetical angle of pitch described by the wing tip of a rollingaerodynamic vehicle along a flight path,

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the vane in this case representing a short span wing. The helix angle iscomputed as where 0' is the helix angle in radians, p is the rollingvelocity in radians/ second, b is the wing span in feet and V is thefree stream flight path velocity in feet/second. From this it will beapparent that the helix angle, represented by the vane 10 displacement 6is constant for a given roll rate and velocity, at Zero angle of attack.

Thus it is clear that the analog voltage output of transducer 14 variesdirectly as p and b and inversely as V. The output of velocity sensor 24is an analog voltage proportional to forward velocity V. In computer 28,the V component from transducer 14 and the V analog voltage fromvelocity sensor 24 are canceled. Mathematically, this cancellation isaccomplished by multiplying by V, dividing both numerator anddenominator by V to get Electronically, if the two analog voltages arecombined degrees out of phase in computer 23, the output will be thedifference in magnitudes and equal to pb T Since [2/2 is a constant, theoutput of computer 28 is proportional to the roll rate, p.

In the stabilization of a ballistic missile, the missile is required toroll at a particular rate at a particular speed to obtain properstability. When the velocity of a missile is known accurately inadvance, the required roll rate and thus the required vane displacementcan be predetermined.

A simple arrangement for controlling a ballistic missile of knownperformance is illustrated in FIGURE 2, in which the vane 10 isconnected to a pick-off or transducer 14 of suitable type, such aselectro-rnechanical, electronic or any other well known device capableof producing an electrical output signal proportional to the angulardisplacement of said vane. The signal from the transducer 14 is fed to acomparator 16, to which is also supplied a signal from a program unit18, the two signals being compared and the resultant error signal isapplied to a servo actuator 20. Rolling of the missile 12 isaccomplished by aerodynamic roll control surfaces 22 pivotally mountedin suitable positions on the missile frame and connected to move inopposition and cause the missile to roll about its longitudinal axis,the principle being well known. The servo actuator 20 may be of anysuitable type, according to the particular requirements of individualmissiles, many different units being readily available.

The program unit 18 is basically a timed mechanism which provides asubstantially continuous signal rate so that, by comparison with thesignal representing the actual roll rate sensed by vane 10, thenecessary corrections can be made to adjust the rollrate to thatrequired. Since the velocity of a missile varies throughout a ballistictrajectory, the rate of roll needed for stable flight changes also. Thusthe program unit 18 provides a signal with the necessary variationstimed to conform to the changes in velocity, which can be accomplishedby a magnetic tape, variable impedance device or mechanical means.

Such programming means are known in the missile art signals andproviding an output signal a error, which is applied to the servoactuator 20. The error signal operates the servo actuator 20 to turn theroll control surfaces 22 through equal and opposite angles 6,, to changethe roll rate of the missile. As the roll rate is corrected, the excessdisplacement of vane is reduced and the offset of roll'control surfaces22 is correspondingly decreased until the roll rate conforms to theprogram.

For more accurate control, or for missiles whose performance may besubject to variation due to unpredictable environment, the more completesystem illustrated in FIGURE 3 may be used. In this arrangement, thevane 10 is connected, as before, to a transducer 14 which provides adisplacement signal a In addition a velocity sensor 24 is utilized tomeasure velocity and is connected to a transducer 26, which provides avelocity signal V. The velocity sensor 24 may be a total head tube orsimilar device mounted on a nose probe or otherwise suitably mounted onthe missile to detect airstream velocity. Both the displacement andVelocity signals are fed to a computer 28, the output of which is asignal representing the measured roll rate, this signal being applied toa comparator 30. Also connected to comparator 30 is a program unit 32which provides a signal proportional to the required value of throughoutthe flight. The two signals are compared and the output of comparator 30is an error signal which is applied to a calibrator 34, in which theerror signal is adjusted to an amplitude suitable for driving the servoactuator 20, through. an amplifier 36, to operate the roll controlsurfaces 22.

The operation of the system is similar to that previously described,except that the instantaneous velocity of the missile is taken intoaccount. Since the helix angle is dependent on both velocity and rollrate, the program unit 32 governs the adjustment of roll rate regardlessof velocity. This is particularly useful for missiles which follow agenerally ballistic trajectory but which require correction at somepoint in the trajectory, either by command signal or an internalprogram. When the missile is rolling at the proper rate relative tovelocity, longitudinal stability is optimum and considerable controlforce is necessary to cause any deviation such as course adjustment. Bydecreasing the roll rate, however, the missile loses a certain amount oflongitudinal stability and may be deviated more easily by simpler andlighter control means. Thus the program unit 32 may be utilized todecrease roll rate andlower stability while a change in trajectory isaccomplished, and afterwards restoring stability by increasing the rollrate to the predetermined level.

The system is applicable as a substitute for rate gyros or angularaccelerometers, which are more costly and complex. The vane 10 is notnecessarily limited to the position ,on the missile as illustrated inFIGURE 1, but can be mounted at any suitable location, dependent on thestructure of the missile and internal arrangement of equipment.Alternatively, the vane 10 may be incorporated into the tip of astabilizing fin, or the like. Further, while the roll control means isillustrated in the form of aerodynamic surfaces, it will be evident thatreaction means such as steering or vernier rockets could be utilized,with suitable connection to the servo actuator.

The operation of this invention will be clearly comprehended from aconsideration of the foregoing description of the mechanical detailsthereof, taken in connection with the drawing and the above recitedobjects. be obvious that all said objects are amply achieved by thisinvention.

It is understood that minor variation from the form of the inventiondisclosed herein may be made without departure from the spirit and scopeof the invention, and that the specification and drawing are to beconsidered as merely illustrative rather than limiting.

I claim:

1. A helix angle sensor and roll control means for use in an aerodynamicbody, comprising: a freely floating, weathercocking vane mounted on thebody to pivot on an axis substantially radial to the longitudinal axisof the body to sense substantially helical airflow due to rotation andforward motion of the body; pick-01f means connected to said vane andproviding a signal proportional to the angular deflection of the vanerelative to the longitudinal axis of the body; velocity sensing meansmounted on the body and providing a signal proportional to thelongitudinal velocity of the body; computer means combining said signalsand providing an output signal proportional to the roll rate of'saidbody; a program unit adapted to provide a signal proportional to therequired roll rate of said body, corresponding to velocity, according toa predetermined program; a comparator connected to said computer and tosaid program unit to compare the signals therefrom and provide an errorsignal proportional to the difference between the signals; actuatingmeans connected to receive and be operated by theerror signal from saidcomparator; and roll control means operatively coupled to said actuatingmeans, whereby said roll control means is moved in accordance with theerror signal to nullify deviation of said vane from that determined bysaid program unit.

2. A helix angle sensor according to claim 1, wherein the roll controlmeans comprises'aerody'namic roll control surfaces pivotallymounted onthe body.

rate and forward velocity and providing an output reference signal;

means combining said comparison and reference signals and providing anoutput error signal proportional to the difference between saidcomparison and reference signals; and

means controlling the roll rate of said bodyactuated by said errorsignal, whereby said error signal corrects the roll rate of said body tocoincide with the predicted roll rate.

References Cited by the Examiner UNITED STATES PATENTS 2,967,679 1/61Owen 244- 77 2,989,270 6/61 Waldow 244 14 SAMUEL 'FEINBERG, PrimaryExaminer. CHESTER L. JUSTUS, Examiner.

It will

1. A HELIX ANGLE SENSOR AND ROLL CONTROL MEANS FOR USE IN AN AERODYNAMICBODY, COMPRISING: A FREELY FLOATING, WEATHERCOCKING VANE MOUNTED ON THEBODY TO PIVOT ON AN AXIS SUBSTANTIALLY RADIAL TO THE LONGITUDINAL AXISOF THE BODY TO SENSE SUBSTANTIALLY HELICAL AIRFLOW DUE TO ROTATION ANDFORWARD MOTION OF THE BODY; PICK-OFF MEANS CONNECTED TO SAID VANE ANDPROVIDING A SIGNAL PROPORTIONAL TO THE ANGULAR DEFLECTION OF THE VANERELATIVE TO THE LONGITUDINAL AXIS OF THE BODY; VELOCITY SENSING MEANSMOUNTED ON THE BODY AND PROVIDING A SIGNAL PROPORTIONAL TO THELONGITUDINAL VELOCITY OF THE BODY; COMPUTER MEANS COMBINING SAID SIGNALSAND PROVIDING AN OUTPUT SIGNAL PROPORTIONAL TO THE ROLL RATE OF SAIDBODY; A PROGRAM UNIT ADAPTED TO PROVIDE A SIGNAL PROPORTIONAL TO THEREQUIRED ROLL RATE OF SAID BODY, CORRESPONDING TO VELOCITY, ACCORDING TOA PREDETERMINED PROGRAM; A COMPARATOR CONNECTED TO SAID COMPUTER AND TOSAID PROGRAM UNIT TO COMPARE THE SIGNALS THEREFROM AND PROVIDE AN ERRORSIGNAL PROPORTIONAL TO THE DIFFERENCE BETWEEN THE SIGNALS; ACTUATINGMEANS CONNECTED TO RECEIVE AND BE OPERATED BY THE ERROR SIGNAL FROM SAIDCOMPARATOR; AND ROLL CONTROL MEANS OPERATIVELY COUPLED TO SAID ACTUATINGMEANS, WHEREBY SAID ROLL CONTROL MEANS IS MOVED IN ACCORDANCE WITH THEERROR SIGNAL TO NULLIFY DEVIATION OF SAID VANE FROM THAT DETERMINED BYSAID PROGRAM UNIT.